#225 Import dialogs throw exceptions when mouse is dragged

[Dave Musicant]

Bring up the ATOFMS or AMS import dialog (same problem
happens for both). Left click on one of the file
selection spaces to pick a file name, but keep the
mouse button down. Drift the mouse away from the space
while keeping the button down, then release. Exceptions
get thrown and we lose stability. True for all file
selection places in both of these dialogs.

Is there anywhere else in Enchilada where this might
happen?